The invention relates to a solid-state trip device for an electrical circuit breaker designed to protect a three-phase mains system, comprising current detection means, delivering analog signals proportional to the currents flowing in the mains system conductors, and an electronic processing unit to which said signals are applied and which delivers a circuit breaker tripping order in the event of preset thresholds being exceeded by said signals.
State-of-the-art trip devices perform conventional protection functions, notably long time delay, short time delay, and instantaneous tripping, and possibly earth fault protection, without making a distinction between faults affecting one or more phases of the system. In a certain number of cases, state-of-the-art trip devices do not provide suitable protection when they treat an unbalanced fault in the same way as a fault affecting the three phases.